Ai BIOLOGICAG’ AND CYTOLOGICAL STUDY OF 
SEX DETERMINATION IN PHYLLOXERANS AND 
APHIDS 
T. H. MORGAN 
Witu One Prate AND TWENTY-THREE FiGures IN TEXT 
PART I 
Inetuxo(liearer Brando; cecnbbocunodomenc Peas a aveinte ep oacvataratatare Mle Siaisyors ays a avaialel stele itnrsicisieyeleiatar sia ers 239 
Sihelitereycle of Ply Memerarte te recta eicie'«\< o\ci)a}risle steret= ene 1s rete ete eal aleheynie\ elo aiaetmds oni le aVni=fele\ tol 243 
Sex determination in Phylloxera fallax...... ora... cece ete ects eee tet eee wee e eee eee enees 244 
Sex determination im Phyloxera Carycccaulis. ee - 1a cfs ce1e.n wleielvinieinfaieieleiainiajei= tials aie) eleielsisaleise)> « 254 
Precocious sexual differences correlated with male and female eggs.............0--+eeeeeeeee 270 
Is the elimination of the sex chromosomes fortuitive or determinative?........-..0e+eeeeeeeee 273 
He liievcyelevotsPhylloxerafallaxcty ers aieio)--seets «l-tefeaieia(e\steiellni staid ale « ble1alolsta elsheloleteteiasel=telelol=ie= 276 
M@hevlitercycle’ of Phylloxerayeamycscaulish 307 <2 opp seve) ci-1< o\eteimore =irlel= w)elolelele anim la)ole)alolsis clel-isiats 290 
Mbeisexaal (> hatiae Ol Chher SRecteh, «05s fae aie + oc: wets nig suialas oa presto ah ein evetela's ainte'>, shale iacuretayss 293 
Spermatogenesisiin aphids.........0.2-.ecececse ence ese sete ete eeeee es eeeeenseeeeteciens 298 
Cytological parallel between P. caryecaulis and Syromastes marginatus .........-.+-+-++++- 305 
PART IT 
Critical review of the recent literature. 
ita PO GLLICEY OTIL ae rept nictevote ee Cee ne ee sania Seer oted ens slic ave on Shal@cst ola tn sjocei sy otatainleresetoyabaherace eveleceratede 306 
Mheieytolowreallieyidence ecm ete sere t ciel ste lsteratela. ol aicyovees\6 Srcieha iol) ares or cie7e whefnieveleys oats) Sin\si aleve Elsie] 307 
The influence of environment on parthenogenetic development.............0-seeeeeeeeeeees 314 
The problem of the three chromosomes... ...:-2- 02. ss0s00- sees cencee tees meses eens nce 322 
‘hey botanical experimental jevidenee’.c op-to.iet- steele s\ciens «jars 21e «| 21a) oreo aye) ovclelelalole eisisjeis\cieleieh= ais 326 
Meadeliant ireatmentwortbessex problemi tic ere cic yelaioia1 2 =\6\ <2) 0'e)siaielel2 ev abel ei steletalatstaiate areolar st 332 
Sex determination as the result of a quantitative relation............-sseseeenceeeeeeeceees 336 
Cyn ANON ISIctets ieseteataters vel feletstenctelahevevereta te = ieiel elas cheinicl-!f-1-/-tetee\etelduetstel=|olojshuiar>|-tst vate 341 
BRE OreLicalw DISC UssIOM sysop tet ete ice tate ee sterrarestay stoi ote ais ver vial ot ste ole halevalere Wielekty fel Spee 344 
anclUsion ante eteysistavo orcestenet ete oreo Ie ia errata hase Lovet ord av aysia sarah avatar atabeter alstetearaynlelnc et e(arevopansieys 348 
PART I 
INTRODUCTION 
The results described in the following pages are the outcome 
of several years’ work. In 1903, when I first began to study the 
aphids, the possibility that sex is determined by external conditions 
was the general opinion of zodlogists. The observations of 
Dageer and Kyber in particular on the aphids seemed to show 
Tue JourNaAL or ExPERIMENTAL ZOOLOGY, VOL, VII, NO. 2. \ 
